A long recognized need exists for suitable recycling methods for polymeric materials, such as thermoplastics. A wide variety of methods have been proposed and attempted. The art has developed to a point at which polymeric materials can be converted into combustible hydrocarbon-containing materials at reasonable material conversion efficiencies. However, while combustible, these hydrocarbon-containing materials may have low economic value due to contaminants derived from the original polymeric or other organic source materials, which are referred to herein as “polymer-derived contaminants” for specifically polymer-derived contaminants, and more generally as “source-derived contaminants” for contaminants originating from the polymeric or other organic source. Such source-derived contaminants include, for example, one or more of an organic chlorine compound, a nitrogen compound, sulfur or an organic or inorganic sulfur compound, color, or an offensive or non-hydrocarbon odor. The presence of such polymer-derived or source-derived contaminants reduces the value of the recovered hydrocarbon-containing materials.
Recent developments have greatly expanded the possible recycled materials which may be the source for such recycled hydrocarbon-containing materials, although such materials still contain source-derived contaminants which need to be removed. For example, as disclosed in “Anything Into Oil”, DISCOVER, Vol. 24, No. 5 (May 2003), waste such as turkey guts can serve as a source for such recycled hydrocarbon-containing materials. As disclosed in this article, many other materials such as manure, crop residuals and polymeric materials such as PVC are considered candidates for recycling by the methods in the article. As noted above, a number of methods exist for recycling polymeric materials by decomposing them to hydrocarbon-containing materials.
As used herein, the term “other organic materials” generally refers to materials such as animal offal, manure, crop residuals and plant material which may be recycled by methods such as described in the above DISCOVER article. As used herein, the term “other organic materials” does not include polymeric materials (such as PET and PVC) and does not include petroleum-derived materials (such as recycled lubricating oils), each of which is separately identified herein.
Although not specifically discussed in the published information regarding such recycling processes as disclosed in the above DISCOVER article, the hydrocarbon-containing materials obtained from these processes are expected to contain contaminants derived from the particular organic source from which the hydrocarbon-containing materials originated. Thus, herein, such contaminants are generally referred to as “source-derived contaminants”. The term “source-derived contaminants” includes any such contaminant originating in the source material, and includes polymer-derived contaminants as a sub-group, and includes other organic-derived contaminants as a sub-group. As used herein, a contaminant is an impurity or other non-hydrocarbon material which detracts from the value of the recycled hydrocarbon-based material for its intended use.
One of the major stumbling blocks in recycling polymeric materials is the need to sort mixed polymeric materials if they are to be directly recycled for use in making new articles from the recycled polymeric material. If polymeric materials could be sorted according to the polymer, they could be more directly recycled into useable polymeric materials, and the problem of contaminants could be reduced or avoided. In most instances, sorting is uneconomically expensive, since it usually requires human action. Thus, recycling polymeric materials has devolved into methods which do not require sorting. In doing so, the various monomers, additives and other chemical species present in the various polymeric materials become combined. As a result, the products obtained from such recycling include a number of the polymer-derived contaminants originating from the various polymers. For example, PVC yields chlorine compounds, nylons yield nitrogen compounds, and polysulfides yield sulfur compounds. The presence of such non-hydrocarbon atoms in the recycled materials contributes to odor, color, corrosivity and other undesirable features of, e.g., recovered hydrocarbon-containing materials.
A number of variables exist with respect to fuels such as diesel fuel. For diesel, such variables include, for example, cetane number, API gravity, BTU content, distillation range, sulfur content, stability and flash point. In addition, in colder weather, cloud point and low temperature filter plugging point may be critical factors. The most important measures of fuel quality include API gravity, heat value (BTU content), distillation range and viscosity. However, these measures relate to conventional diesel fuels obtained from petroleum refining. Hydrocarbon materials obtained from other sources, such as recycled polymeric materials or recycled lubricating oils, fuels, etc., may contain contaminants, such as those noted above, and/or other outside-specification materials, such as high- or low-boiling constituents, which are not normally found in hydrocarbon fractions or finished fuels obtained from conventional petroleum sources.
Recycled hydrocarbon-containing materials may have a heat content, e.g., about 19,000 BTU/pound or higher, sufficient for use as a fuel. Typical diesel fuel has a lower heating value of 132,000 BTU/gal (36.6 MJ/L), which corresponds to about 19,050 BTU/lb at 6.93 lb/gal at sp. gr. 0.83 for diesel fuel.
However, in spite of suitable heat value, recycled hydrocarbon-containing materials generally have such low commercial value as to make the overall recycling process unprofitable. The reason these recycled hydrocarbon-containing materials have such low commercial value is that the materials include high levels of the above-noted contaminants which are residuals from the sources, such as polymeric materials or other sources. Such contaminants make the hydrocarbon-containing materials unsuitable for use in motor vehicle engines or in other uses in which the content of the source-derived contaminants result in problems with equipment (e.g., chlorine compounds), or environmental problems (e.g., nitrogen compounds, sulfur and sulfur compounds), or problems with consumer acceptance (e.g., extremely disagreeable and/or non-hydrocarbon odor). An additional problem with such recycled polymeric materials is that the combustible hydrocarbon material obtained often one or more off-specification characteristic relating to use as a motor vehicle fuel. For example, a fuel intended for use as a diesel fuel may have an unacceptably low or high flash point for its intended use. Such fuels may be useful for some purposes, but refinery-grade fuels generally include a narrower range of materials. The many high- or low-molecular weight materials in such recycled polymeric materials may make the combustible hydrocarbon unsuitable for use as a motor vehicle fuel. In addition, the hydrocarbon-containing materials may have a noxious scent, and in some cases, the noxious scent may be so bad as to render the materials valueless or at least to substantially reduce their value.
As a result of such deficiencies, currently available recycled hydrocarbon-containing materials obtained from polymeric materials such as thermoplastics, or from other organic materials such as turkey offal, may have a commercial value which is lower than the costs of recovering such materials, making it uneconomical and undesirable to attempt to recover such materials. Such deficiencies with the currently available combustible hydrocarbon materials obtained from recycled polymeric materials may reduce the value of the combustible hydrocarbon material to, e.g, about US$0.20/US gallon (at the time of filing this application), which may mean that the recycling is unprofitable.
Clay filtration has been used to clean up oils recovered from crankcase oils, hydraulic oils and other used oil sources. However, such processes generally require the presence of special treatment steps, the use of additives such as catalysts, solubilizing agents, etc. Such processes have not been applied to materials such as hydrocarbon-containing materials obtained from thermal decomposition of polymeric and other recycled materials, in which the hydrocarbon-containing materials comprise one or more source-derived contaminant.
In addition to processes for recycling polymeric materials such as thermoplastics, there has existed at least since the dawn of the automobile era a need for recycling lubricating materials associated with automobiles, trucks, and other combustion based engines such as locomotive engines and ship engines. Such lubricating materials include, for example, engine crankcase oil, lubricating oil, transmission oil, gear oil, and similar petroleum-based or synthetic hydrocarbon lubricating materials.
A number of processes have been developed for recycling such petroleum-based or synthetic hydrocarbon lubricating materials. As with the recycling of polymeric materials, these processes generally leave something to be desired, such as low efficiency, low usability or low user/consumer acceptability of the products. For example, in order to obtain a motor vehicle-usable grade fuel from such sources, it is often necessary to remove contaminants which may include additives, and decomposition products and heavy metals accumulated in the lubricant during its use, and it is often necessary to “crack” such hydrocarbon materials in order to obtain lower molecular weight components. As is known, cracking may require the presence of hydrogen and also may result in the formation of heavy tars and coke. When such lubricating materials are mixed together and recycled, due to the high molecular weight components, the flash point of the resulting recycled hydrocarbon material may be too high to be useful as a fuel for automobiles, trucks and other land vehicles, leaving only low-grade uses, such as bunker fuel as a possible use.
Accordingly, a need exists for processes which are capable of removing the contaminants from combustible hydrocarbon-containing materials obtained from recycled polymeric materials, in which the processes are economical and are capable of producing a fuel suitable for use in a motor vehicle, and in particular for processes which are capable of producing a refinery-grade fuel such as diesel which meets the appropriate ASTM, API and/or SAE standards.